To everything, there is a season—even IOP rise. Researchers recently found that pressure measures taken in the winter were higher than those taken in the summer in both normal and primary open-angle glaucoma (POAG) eyes. They noted that this seasonal IOP fluctuation had a significant impact on RNFL thinning progression, or lack of. They suggest that a temporary decline in IOP in the summer, rather than a constant IOP throughout the year, may prevent disease progression.

The study included 12,686 normal eyes and 179 POAG eyes that had a significantly higher IOP in the winter than in the summer (normal: 13.2mm Hg vs. 12.5mm Hg, POAG: 13.1mm Hg vs. 11.8mm Hg). The rate of RNFL thinning was -0.44μm/year, with 47.5% of POAG eyes showing RNFL thinning progression. The investigators’ analysis showed that a high seasonal IOP fluctuation rate significantly suppressed RNFL thinning and that a low seasonal fluctuation rate was an independent risk factor for the progression of RNFL thinning.

While the team reported that a high IOP in the winter and a lower IOP in the summer suppress glaucoma progression, this finding appeared to be non-intuitive, as high IOP, regardless of the season, usually adversely affects glaucoma progression. The authors speculate that the positive effect of a low IOP in the summer may be stronger than the negative effect of a high IOP in the winter.